<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    function People(name, age, sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    People.prototype.nationality = '中国';

    var xm = new People('小明', 12, '男');
    console.log(People.prototype);
    console.log(xm.__proto__);
    console.log(xm.nationality);
</script>
</body>
</html>